The present invention relates to elevators and, more particularly, to electronic safety detection systems for elevator doors.
In elevator installations, many automatic sliding doors are equipped with safety systems designed to detect potential interference with the closing operation of the doors. Such safety systems typically include a plurality of signal emitter sources disposed on one door, and a plurality of signal receiver sources disposed on the other door. The signal emitters emit a curtain of signals across the threshold of the elevator door which are received by the signal receivers. When the curtain of signals is interrupted, the safety system communicates with a door controller in order to either stop the door closing operation and open the doors, or to maintain the doors in an opened position, depending on the current door position.
A doorway safety system is described in U.S. Pat. No. 4,029,176 (Mills) that utilizes acoustic wave transmitters and receivers to detect objects or persons within an area near the elevator doors. The system detects objects positioned between the doors and across the threshold, and extends the zone of detection into the entryway. The transmitters send out a signal at an angle into the entryway. When an obstruction enters the detection zone, the signal reflects from the obstruction and is detected by the receivers.
Another doorway safety system described in U.S. Pat. No, 5,886,307 (Full et al.) discloses a three-dimensional system for detecting objects across the threshold and in the entryway. The system projects a curtain of light beams across the threshold and illuminates the area directly in front of the entryway with three-dimensional detection beams. The system detects obstructions between the doors and across the threshold if an obstruction breaks one or more of the beams. In addition, if energy from the three-dimensional beams reflects off of an object in the entryway into the three-dimensional receivers, the obstruction is also detected.
The above-described system for three-dimensional detection has significant shortcomings. For example, while curtain-type detection systems require a xe2x80x9cbreakxe2x80x9d in one or more curtain beams to indicate an obstruction across a threshold, three-dimensional detection requires a xe2x80x9cconnectxe2x80x9d to indicate an obstruction. This inverted logic for three-dimensional detection results in a sensitivity to external sources of energy that are not problematic in single-plane or curtain-type detection systems.
Systems that use light as the energy source for three-dimensional detection are subject to interference from a variety of external sources. For example, sources of light external to the detection system located near the elevator installation can inadvertently be picked up by the light sensors of the detection system. If the light from an external source is modulated similarly to that transmitted by the door safety system, it can be picked up and interpreted as indicative of an obstruction. Such external sources of light may include fluorescent lighting systems, emergency strobe lights, and emergency vehicle beacons.
External sources of impulse-type, electrical noise may also result in inadvertent obstruction signaling in three-dimensional door safety systems. Sources of this type of electrical noise include relay type elevator controllers, as well as electro-mechanical door operators.
It is an object of the present invention to provide an improved, three-dimensional door safety detection system for sliding doors.
It is another object of the present invention to provide a three-dimensional door safety detection system that is reliably operable in the presence of impulse-type electrical noise.
It is yet another object of the present invention to provide a three-dimensional door safety detection system that is reliably operable in the presence of external light sources, including sources that produce light energy having characteristics similar to the light energy produced by the detection system.
These objects and others are achieved by the present invention as described herein.
The present invention is directed to a three-dimensional door safety system for detecting objects or persons approaching or in a predetermined safety zone of open doors. A plurality of receivers or detectors are located on one door, and a plurality of emitters are located on the opposite door. The area directly in front of the closing doors is scanned for obstructions. The safety system detects objects in the entryway, while distinguishing from external energy that is not produced by the safety system. Generally, each beam produced by the energy emitters is sampled. The amplitude of each respective beam is stored. The amplitudes are each compared to a predetermined detection threshold level to determine the presence or absence of objects in the detection area.
The first embodiment of the present invention takes into account the transitory nature of interference energy, where the interference is present for a very short period, then becomes undetectable. In this embodiment, each three-dimensional beam is sampled multiple times per door scan frame. The value of the smallest amplitude sample acquired is compared with the detection threshold level to determine the presence or absence of objects in the three-dimensional detection area. This embodiment effectively ignores most impulse-type interference, such as electrical noise spikes, and light produced by strobe lamps.
A second embodiment of the present invention also accounts for the transitory nature of interference energy. In this case, however, the interference energy continues to be detectable beyond the high amplitude portion of the interference signal. In this embodiment, each three-dimensional beam is sampled multiple times per door scan frame. The value of each sample is stored for the respective beam. Detection energy, reflecting from an object in the three-dimensional detection area should present a generally constant, i.e., within a predetermined maximum variance range, amplitude from sample to sample, within a single scan frame, for any particular beam. If the samples for any particular beam do not present this constant signature, the energy for that beam is considered to be interference energy and is ignored. This embodiment improves the discrimination capability of the first embodiment by providing the ability to ignore interference energy that is continuously detectable but inconsistent in amplitude, such as the light produced by some fluorescent lighting systems.
A third embodiment of the present invention assigns an identifier to the emitted energy to provide the ability to reject interference energy that is both continuously detectable and consistent in amplitude. In this embodiment, each three-dimensional beam is sampled a single time per door scan frame while the transmitted energy is produced with unique, verifiable modulation, i.e., a modulation code, that can be validated by the detection receiver. If the modulation code is detected in the sampled beam, a signal is generated indicating the presence of an object. If the modulation code of the detected energy received for a particular beam is not verified by the receiver, the detected energy for that beam is ignored, as interference energy, regardless of its amplitude. This embodiment provides the ability to reject interference energy that cannot be rejected by the first and second embodiments because the interference energy is continuously detectable and relatively constant in amplitude, such as light produced by some fluorescent lighting systems.
Alternate embodiments of the present invention could use various combinations of the approaches described above with respect to the three preferred embodiments. By combining the various approaches, the ability to discriminate between target detection energy and interference energy from external sources is enhanced.
Because of the sensitivity to external sources of light and impulse noise introduced by the addition of three-dimensional detection capability to door safety systems, some prior art systems are rendered inoperable under various conditions. Such conditions include elevator installations that utilize relay-type controllers, fire alarm systems that utilize strobe lights, installations in the vicinity of emergency vehicle beacons (i.e., hospitals), and installations near fluorescent lighting systems. The present invention provides a system that is reliably operable in such environments and, thus, more safe and economically operable.